The present invention relates in general to electronic locking devices and in particular to a locking device of the type having pulse-operated, inductively interacting key and lock parts, the lock part being connectable to an object to be locked and including bolt means activatable exclusively in response to an assigned key part so as to move between an operative and inoperative position, at least the lock part generating, in response to a start pulse, a sequence of digital input data in the form of electrical pulses which are applied to the key part. The key part and the lock part being provided each with specific association between the unanimous input data at respective lock and key parts, and between output data in the form of electrical pulses generated by the two parts, the specific associations being relative only for the key and lock parts which belong one to another and serve as an electric code for the latter, and a common comparator arranged at least in the lock part for comparing the pulse sequences of the output data, and for generating an actuation pulse for the bolt means when the two pulse sequences are correlative or in mutual agreement.
In the known locking devices of this kind, described for example in the German publication No. 2,234,815 and in U.S. Pat. No. 3,761,892, a starting switch is provided at the lock part and after actuation of this switch an oscillator in cooperation with a counter produces all possible permutations of a number system and feeds the entire body of numbers in the form of electrical pulses to a read-only memory in the lock part and also to the memory in the interfacing key part. This sequence of pulses determines the input addresses for the two read-only memories (ROM). At these addresses, each ROM stores unambiguously output magnitudes which are applied again in the form of electrical pulses to one of two inputs of a comparator. The comparator tests the correlation of the output signals incoming from the key and lock parts and actuates the electromagnetic apparatus of the bolt means only then when the two output signals are unanimous. The specific stored information in the two read-only memories is the electrical codes for the key and lock parts which belong one to the other. This code is individual for each matching pair of the key and lock subunits and is different for all remaining pairs. The output signal from the two ROM's is also a definite number from this body of numbers.
A disadvantage of these known locking devices is the fact that the key part can be relatively easily copied. An unauthorized person, after the actuation of the start switch on the lock part, can record the entire sequence of pulses and, when he or she gains momentary access to the corresponding key part, the sequence of the output signal at the key part can also be recorded and the electronic code is thus broken. The unauthorized person thereafter can easily produce a second key. Even when using a very large "body of numbers" for the input and output signals, the safety of these known locking devices is not considerably increased and, in addition, a further disadvantage is produced due to excessive time consumption for the transfer of such long pulse sequences.
In processes for transferring data between two stations, disclosed for example in European patent application No. 0,002,580, it has been disclosed how to generate in a first station a random number from which a coded test number is derived and transferred to a second station where the decoding takes place. The communication between the two stations thus necessitates cumbersome coding and decoding operations and the application of this data transmission to electronic locking devices having individually coded key and lock parts is not advantageous.
The same is true for another known communications device described in German publication No. 2,253,275, in which the access to the device by unauthorized persons is protected in such a manner that a code word is necessary in addition to the electronic key part. In the device a group of random numbers is generated, but this group serves for the selection of a definite code on both sides. This code is used both for locking and key parts of the locking device (German publication No. 2,635,180, U.S. Pat. No. 4,209,782) where according to the law of probability the electronic code in a pair of lock and key parts is changed. When the correspondence of the code is detected during application, then a new code pair is assigned to the lock and key parts. In this case, the random number immediately produces an electronic code which, after each application is changed in the key and lock pair.